/*
  Copyright 2011-2020 David Robillard <d@drobilla.net>

  Permission to use, copy, modify, and/or distribute this software for any
  purpose with or without fee is hereby granted, provided that the above
  copyright notice and this permission notice appear in all copies.

  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

#include "byte_sink.h"
#include "env.h"
#include "node.h"
#include "sink.h"
#include "string_utils.h"
#include "system.h"
#include "uri_utils.h"
#include "world.h"

#include "serd/serd.h"

#include <assert.h>
#include <errno.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifndef _MSC_VER
#  define SERD_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
#else
#  define SERD_WARN_UNUSED_RESULT
#endif

#define TRY(st, exp)      \
  do {                    \
    if (((st) = (exp))) { \
      return (st);        \
    }                     \
  } while (0)

typedef enum {
  CTX_NAMED, ///< Normal non-anonymous context
  CTX_BLANK, ///< Anonymous blank node
  CTX_LIST   ///< Anonymous list
} ContextType;

typedef struct {
  ContextType        type;
  SerdStatementFlags flags;
  SerdNode*          graph;
  SerdNode*          subject;
  SerdNode*          predicate;
  bool               indented_object;
} WriteContext;

static const WriteContext WRITE_CONTEXT_NULL =
  {CTX_NAMED, 0, NULL, NULL, NULL, false};

static const size_t anon_stack_capacity = SERD_PAGE_SIZE / sizeof(WriteContext);

typedef enum {
  SEP_NONE,        ///< Placeholder for nodes or nothing
  SEP_END_S,       ///< End of a subject ('.')
  SEP_END_P,       ///< End of a predicate (';')
  SEP_END_O,       ///< End of an object (',')
  SEP_S_P,         ///< Between a subject and predicate (whitespace)
  SEP_P_O,         ///< Between a predicate and object (whitespace)
  SEP_ANON_BEGIN,  ///< Start of anonymous node ('[')
  SEP_ANON_S_P,    ///< Between start of anonymous node and predicate
  SEP_ANON_END,    ///< End of anonymous node (']')
  SEP_LIST_BEGIN,  ///< Start of list ('(')
  SEP_LIST_SEP,    ///< List separator (newline)
  SEP_LIST_END,    ///< End of list (')')
  SEP_TLIST_BEGIN, ///< Start of terse list ('(')
  SEP_TLIST_SEP,   ///< Terse list separator (space)
  SEP_TLIST_END,   ///< End of terse list (')')
  SEP_GRAPH_BEGIN, ///< Start of graph ('{')
  SEP_GRAPH_END,   ///< End of graph ('}')
} Sep;

typedef uint32_t SepMask; ///< Bitfield of separator flags

#define SEP_ALL ((SepMask)-1)
#define M(s) (1U << (s))

typedef struct {
  const char* str;             ///< Sep string
  size_t      len;             ///< Length of sep string
  int         indent;          ///< Indent delta
  SepMask     pre_space_after; ///< Leading space if after given seps
  SepMask     pre_line_after;  ///< Leading newline if after given seps
  SepMask     post_line_after; ///< Trailing newline if after given seps
} SepRule;

static const SepRule rules[] = {
  {"", 0, +0, SEP_NONE, SEP_NONE, SEP_NONE},
  {".\n", 2, -1, SEP_ALL, SEP_NONE, SEP_NONE},
  {";", 1, +0, SEP_ALL, SEP_NONE, SEP_ALL},
  {",", 1, +0, SEP_ALL, SEP_NONE, ~(M(SEP_ANON_END) | M(SEP_LIST_END))},
  {"", 0, +1, SEP_NONE, SEP_NONE, SEP_ALL},
  {" ", 1, +0, SEP_NONE, SEP_NONE, SEP_NONE},
  {"[", 1, +1, M(SEP_END_O), M(SEP_TLIST_BEGIN) | M(SEP_TLIST_SEP), SEP_NONE},
  {"", 0, +0, SEP_NONE, SEP_ALL, SEP_NONE},
  {"]", 1, -1, SEP_NONE, ~M(SEP_ANON_BEGIN), SEP_NONE},
  {"(", 1, +1, M(SEP_END_O), SEP_NONE, SEP_ALL},
  {"", 0, +0, SEP_NONE, SEP_ALL, SEP_NONE},
  {")", 1, -1, SEP_NONE, SEP_ALL, SEP_NONE},
  {"(", 1, +1, SEP_NONE, SEP_NONE, SEP_NONE},
  {"", 0, +0, SEP_ALL, SEP_NONE, SEP_NONE},
  {")", 1, -1, SEP_NONE, SEP_NONE, SEP_NONE},
  {"{", 1, +1, SEP_ALL, SEP_NONE, SEP_NONE},
  {"}", 1, -1, SEP_NONE, SEP_NONE, SEP_ALL},
  {"<", 1, +0, SEP_NONE, SEP_NONE, SEP_NONE},
  {">", 1, +0, SEP_NONE, SEP_NONE, SEP_NONE},
};

struct SerdWriterImpl {
  SerdWorld*      world;
  SerdSink        iface;
  SerdSyntax      syntax;
  SerdWriterFlags flags;
  SerdEnv*        env;
  SerdNode*       root_node;
  SerdURIView     root_uri;
  WriteContext*   anon_stack;
  size_t          anon_stack_size;
  SerdByteSink*   byte_sink;
  SerdErrorFunc   error_func;
  void*           error_handle;
  WriteContext    context;
  char*           bprefix;
  size_t          bprefix_len;
  Sep             last_sep;
  int             indent;
  bool            empty;
};

typedef enum { WRITE_STRING, WRITE_LONG_STRING } TextContext;

static SerdStatus
serd_writer_set_prefix(SerdWriter*     writer,
                       const SerdNode* name,
                       const SerdNode* uri);

SERD_WARN_UNUSED_RESULT static SerdStatus
write_node(SerdWriter*        writer,
           const SerdNode*    node,
           SerdField          field,
           SerdStatementFlags flags);

static bool
supports_abbrev(const SerdWriter* writer)
{
  return writer->syntax == SERD_TURTLE || writer->syntax == SERD_TRIG;
}

static bool
supports_uriref(const SerdWriter* writer)
{
  return writer->syntax == SERD_TURTLE || writer->syntax == SERD_TRIG;
}

static SerdStatus
free_context(SerdWriter* writer)
{
  serd_node_free(writer->context.graph);
  serd_node_free(writer->context.subject);
  serd_node_free(writer->context.predicate);
  return SERD_SUCCESS;
}

static SerdStatus
push_context(SerdWriter* const        writer,
             const ContextType        type,
             const SerdStatementFlags flags,
             const SerdNode* const    g,
             const SerdNode* const    s,
             const SerdNode* const    p)
{
  if (writer->anon_stack_size >= anon_stack_capacity) {
    return SERD_ERR_OVERFLOW;
  }

  const WriteContext new_context = {type,
                                    flags,
                                    serd_node_copy(g),
                                    serd_node_copy(s),
                                    serd_node_copy(p),
                                    false};

  writer->anon_stack[writer->anon_stack_size++] = writer->context;
  writer->context                               = new_context;
  return SERD_SUCCESS;
}

static inline void
pop_context(SerdWriter* writer)
{
  assert(writer->anon_stack_size > 0);

  if (writer->context.indented_object && writer->indent > 0) {
    --writer->indent;
  }

  free_context(writer);
  writer->context = writer->anon_stack[--writer->anon_stack_size];
}

static inline SerdNode*
ctx(SerdWriter* writer, const SerdField field)
{
  SerdNode* node = NULL;
  if (field == SERD_SUBJECT) {
    node = writer->context.subject;
  } else if (field == SERD_PREDICATE) {
    node = writer->context.predicate;
  } else if (field == SERD_GRAPH) {
    node = writer->context.graph;
  }

  return node && node->type ? node : NULL;
}

SERD_WARN_UNUSED_RESULT static inline size_t
sink(const void* buf, size_t len, SerdWriter* writer)
{
  const size_t written = serd_byte_sink_write(buf, len, writer->byte_sink);
  if (written != len) {
    if (errno) {
      serd_world_errorf(writer->world,
                        SERD_ERR_BAD_WRITE,
                        "write error (%s)\n",
                        strerror(errno));
    } else {
      serd_world_errorf(writer->world, SERD_ERR_BAD_WRITE, "write error\n");
    }
  }

  return written;
}

SERD_WARN_UNUSED_RESULT static inline SerdStatus
esink(const void* buf, size_t len, SerdWriter* writer)
{
  return sink(buf, len, writer) == len ? SERD_SUCCESS : SERD_ERR_BAD_WRITE;
}

// Write a single character, as an escape for single byte characters
// (Caller prints any single byte characters that don't need escaping)
SERD_WARN_UNUSED_RESULT static size_t
write_character(SerdWriter*    writer,
                const uint8_t* utf8,
                size_t*        size,
                SerdStatus*    st)
{
  char           escape[11] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
  const uint32_t c          = parse_utf8_char(utf8, size);
  switch (*size) {
  case 0:
    serd_world_errorf(
      writer->world, SERD_ERR_BAD_ARG, "invalid UTF-8 start: %X\n", utf8[0]);
    *st = SERD_ERR_BAD_TEXT;
    return 0;
  case 1:
    snprintf(escape, sizeof(escape), "\\u%04X", utf8[0]);
    return sink(escape, 6, writer);
  default:
    break;
  }

  if (!(writer->flags & SERD_WRITE_ASCII)) {
    // Write UTF-8 character directly to UTF-8 output
    return sink(utf8, *size, writer);
  }

  if (c <= 0xFFFF) {
    snprintf(escape, sizeof(escape), "\\u%04X", c);
    return sink(escape, 6, writer);
  }

  snprintf(escape, sizeof(escape), "\\U%08X", c);
  return sink(escape, 10, writer);
}

static inline bool
uri_must_escape(const char c)
{
  switch (c) {
  case ' ':
  case '"':
  case '<':
  case '>':
  case '\\':
  case '^':
  case '`':
  case '{':
  case '|':
  case '}':
    return true;
  default:
    return !in_range(c, 0x20, 0x7E);
  }
}

static size_t
write_uri(SerdWriter* writer, const char* utf8, size_t n_bytes, SerdStatus* st)
{
  size_t len = 0;
  for (size_t i = 0; i < n_bytes;) {
    size_t j = i; // Index of next character that must be escaped
    for (; j < n_bytes; ++j) {
      if (uri_must_escape(utf8[j])) {
        break;
      }
    }

    // Bulk write all characters up to this special one
    const size_t n_bulk = sink(&utf8[i], j - i, writer);
    len += n_bulk;
    if (n_bulk != j - i) {
      return len;
    }

    if ((i = j) == n_bytes) {
      break; // Reached end
    }

    // Write UTF-8 character
    size_t size = 0;
    len += write_character(writer, (const uint8_t*)utf8 + i, &size, st);
    i += size;
    if (*st && !(writer->flags & SERD_WRITE_LAX)) {
      break;
    }

    if (size == 0) {
      // Corrupt input, write percent-encoded byts and scan to next start
      char escape[4] = {0, 0, 0, 0};
      for (; i < n_bytes && (utf8[i] & 0x80); ++i) {
        snprintf(escape, sizeof(escape), "%%%02X", (uint8_t)utf8[i]);
        len += sink(escape, 3, writer);
      }
    }
  }

  return len;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
ewrite_uri(SerdWriter* writer, const char* utf8, size_t n_bytes)
{
  SerdStatus st = SERD_SUCCESS;
  write_uri(writer, utf8, n_bytes, &st);

  return (writer->flags & SERD_WRITE_LAX) ? SERD_SUCCESS : st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_uri_from_node(SerdWriter* writer, const SerdNode* node)
{
  return ewrite_uri(writer, serd_node_string(node), node->n_bytes);
}

static bool
lname_must_escape(const char c)
{
  /* This arbitrary list of characters, most of which have nothing to do with
     Turtle, must be handled as special cases here because the RDF and SPARQL
     WGs are apparently intent on making the once elegant Turtle a baroque
     and inconsistent mess, throwing elegance and extensibility completely
     out the window for no good reason.

     Note '-', '.', and '_' are also in PN_LOCAL_ESC, but are valid unescaped
     in local names, so they are not escaped here. */

  switch (c) {
  case '\'':
  case '!':
  case '#':
  case '$':
  case '%':
  case '&':
  case '(':
  case ')':
  case '*':
  case '+':
  case ',':
  case '/':
  case ';':
  case '=':
  case '?':
  case '@':
  case '~':
    return true;
  default:
    break;
  }
  return false;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_lname(SerdWriter* writer, const char* utf8, size_t n_bytes)
{
  SerdStatus st = SERD_SUCCESS;
  for (size_t i = 0; i < n_bytes; ++i) {
    size_t j = i; // Index of next character that must be escaped
    for (; j < n_bytes; ++j) {
      if (lname_must_escape(utf8[j])) {
        break;
      }
    }

    // Bulk write all characters up to this special one
    TRY(st, esink(&utf8[i], j - i, writer));
    if ((i = j) == n_bytes) {
      break; // Reached end
    }

    // Write escape
    TRY(st, esink("\\", 1, writer));
    TRY(st, esink(&utf8[i], 1, writer));
  }

  return st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_text(SerdWriter* writer,
           TextContext ctx,
           const char* utf8,
           size_t      n_bytes)
{
  size_t     len                  = 0;
  size_t     n_consecutive_quotes = 0;
  SerdStatus st                   = SERD_SUCCESS;
  for (size_t i = 0; i < n_bytes;) {
    if (utf8[i] != '"') {
      n_consecutive_quotes = 0;
    }

    // Fast bulk write for long strings of printable ASCII
    size_t j = i;
    for (; j < n_bytes; ++j) {
      if (utf8[j] == '\\' || utf8[j] == '"' ||
          (!in_range(utf8[j], 0x20, 0x7E))) {
        break;
      }
    }

    len += sink(&utf8[i], j - i, writer);
    if ((i = j) == n_bytes) {
      break; // Reached end
    }

    const char in = utf8[i++];
    if (ctx == WRITE_LONG_STRING) {
      n_consecutive_quotes = (in == '\"') ? (n_consecutive_quotes + 1) : 0;

      switch (in) {
      case '\\':
        len += sink("\\\\", 2, writer);
        continue;
      case '\b':
        len += sink("\\b", 2, writer);
        continue;
      case '\n':
      case '\r':
      case '\t':
      case '\f':
        len += sink(&in, 1, writer); // Write character as-is
        continue;
      case '\"':
        if (n_consecutive_quotes >= 3 || i == n_bytes) {
          // Two quotes in a row, or quote at string end, escape
          len += sink("\\\"", 2, writer);
        } else {
          len += sink(&in, 1, writer);
        }
        continue;
      default:
        break;
      }
    } else if (ctx == WRITE_STRING) {
      switch (in) {
      case '\\':
        len += sink("\\\\", 2, writer);
        continue;
      case '\n':
        len += sink("\\n", 2, writer);
        continue;
      case '\r':
        len += sink("\\r", 2, writer);
        continue;
      case '\t':
        len += sink("\\t", 2, writer);
        continue;
      case '"':
        len += sink("\\\"", 2, writer);
        continue;
      default:
        break;
      }
      if (writer->syntax == SERD_TURTLE) {
        switch (in) {
        case '\b':
          len += sink("\\b", 2, writer);
          continue;
        case '\f':
          len += sink("\\f", 2, writer);
          continue;
        default:
          break;
        }
      }
    }

    // Write UTF-8 character
    size_t size = 0;
    len += write_character(writer, (const uint8_t*)utf8 + i - 1, &size, &st);
    if (st && !(writer->flags & SERD_WRITE_LAX)) {
      return st;
    }

    if (size == 0) {
      // Corrupt input, write repacement character and scan to the next start
      len += sink(replacement_char, sizeof(replacement_char), writer);
      for (; i < n_bytes && (utf8[i] & 0x80); ++i) {
      }
    } else {
      i += size - 1;
    }
  }

  return (writer->flags & SERD_WRITE_LAX) ? SERD_SUCCESS : st;
}

typedef struct {
  SerdWriter* writer;
  SerdStatus  status;
} UriSinkContext;

SERD_WARN_UNUSED_RESULT static size_t
uri_sink(const void* buf, size_t size, size_t nmemb, void* stream)
{
  (void)size;
  assert(size == 1);

  UriSinkContext* const ctx    = (UriSinkContext*)stream;
  SerdWriter* const     writer = ctx->writer;

  return write_uri(writer, (const char*)buf, nmemb, &ctx->status);
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_newline(SerdWriter* writer, bool terse)
{
  if (terse || (writer->flags & SERD_WRITE_TERSE)) {
    return esink(" ", 1, writer);
  }

  SerdStatus st = SERD_SUCCESS;
  TRY(st, esink("\n", 1, writer));
  for (int i = 0; i < writer->indent; ++i) {
    TRY(st, esink("\t", 1, writer));
  }

  return st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_top_level_sep(SerdWriter* writer)
{
  return ((!writer->empty && !(writer->flags & SERD_WRITE_TERSE))
            ? write_newline(writer, false)
            : SERD_SUCCESS);
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_sep(SerdWriter* writer, const SerdStatementFlags flags, Sep sep)
{
  SerdStatus     st    = SERD_SUCCESS;
  const SepRule* rule  = &rules[sep];
  const bool     terse = (((flags & SERD_TERSE_S) && (flags & SERD_LIST_S)) ||
                      ((flags & SERD_TERSE_O) && (flags & SERD_LIST_O)));
  if (terse && sep >= SEP_LIST_BEGIN && sep <= SEP_LIST_END) {
    sep = (Sep)((int)sep + 3); // Switch to corresponding terse separator
  }

  // Adjust indent, but tolerate if it would become negative
  if ((rule->pre_line_after & (1u << writer->last_sep) ||
       (rule->post_line_after & (1u << writer->last_sep)))) {
    writer->indent = ((rule->indent >= 0 || writer->indent >= -rule->indent)
                        ? writer->indent + rule->indent
                        : 0);
  }

  // Write newline or space before separator if necessary
  if (rule->pre_line_after & (1u << writer->last_sep)) {
    TRY(st, write_newline(writer, terse));
  } else if (rule->pre_space_after & (1u << writer->last_sep)) {
    TRY(st, esink(" ", 1, writer));
  }

  // Write actual separator string
  if (rule->len > 0) {
    TRY(st, esink(rule->str, rule->len, writer));
  }

  // Write newline after separator if necessary
  if (rule->post_line_after & (1u << writer->last_sep)) {
    TRY(st, write_newline(writer, terse));
    writer->last_sep = SEP_NONE;
  } else {
    writer->last_sep = sep;
  }

  if (sep == SEP_END_S) {
    writer->indent = 0;
  }

  return st;
}

static void
reset_context(SerdWriter* writer, bool graph)
{
  // Free any lingering contexts in case there was an error
  while (writer->anon_stack_size > 0) {
    pop_context(writer);
  }

  if (graph && writer->context.graph) {
    memset(writer->context.graph, 0, sizeof(SerdNode));
  }

  if (writer->context.subject) {
    memset(writer->context.subject, 0, sizeof(SerdNode));
  }

  if (writer->context.predicate) {
    memset(writer->context.predicate, 0, sizeof(SerdNode));
  }

  writer->anon_stack_size         = 0;
  writer->context.indented_object = false;
  writer->empty                   = false;
}

static bool
is_inline_start(const SerdWriter*  writer,
                SerdField          field,
                SerdStatementFlags flags)
{
  return (supports_abbrev(writer) &&
          ((field == SERD_SUBJECT && (flags & SERD_ANON_S)) ||
           (field == SERD_OBJECT && (flags & SERD_ANON_O))));
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_literal(SerdWriter*        writer,
              const SerdNode*    node,
              SerdStatementFlags flags)
{
  writer->last_sep = SEP_NONE;

  const SerdNode* datatype = serd_node_datatype(node);
  const SerdNode* lang     = serd_node_language(node);
  const char*     node_str = serd_node_string(node);
  const char*     type_uri = datatype ? serd_node_string(datatype) : NULL;
  if (supports_abbrev(writer) && type_uri) {
    if (serd_node_equals(datatype, writer->world->xsd_boolean) ||
        serd_node_equals(datatype, writer->world->xsd_integer)) {
      return esink(node_str, node->n_bytes, writer);
    }

    if (serd_node_equals(datatype, writer->world->xsd_decimal) &&
        strchr(node_str, '.') && node_str[node->n_bytes - 1] != '.') {
      /* xsd:decimal literals without trailing digits, e.g. "5.", can
         not be written bare in Turtle.  We could add a 0 which is
         prettier, but changes the text and breaks round tripping.
      */
      return esink(node_str, node->n_bytes, writer);
    }
  }

  SerdStatus st = SERD_SUCCESS;
  if (supports_abbrev(writer) &&
      (node->flags & (SERD_HAS_NEWLINE | SERD_HAS_QUOTE))) {
    TRY(st, esink("\"\"\"", 3, writer));
    TRY(st, write_text(writer, WRITE_LONG_STRING, node_str, node->n_bytes));
    TRY(st, esink("\"\"\"", 3, writer));
  } else {
    TRY(st, esink("\"", 1, writer));
    TRY(st, write_text(writer, WRITE_STRING, node_str, node->n_bytes));
    TRY(st, esink("\"", 1, writer));
  }
  if (lang && serd_node_string(lang)) {
    TRY(st, esink("@", 1, writer));
    TRY(st, esink(serd_node_string(lang), lang->n_bytes, writer));
  } else if (type_uri) {
    TRY(st, esink("^^", 2, writer));
    return write_node(writer, datatype, (SerdField)-1, flags);
  }
  return st;
}

// Return true iff `buf` is a valid prefixed name prefix or suffix
static inline bool
is_name(const char* buf, const size_t len)
{
  // TODO: This is more strict than it should be
  for (size_t i = 0; i < len; ++i) {
    if (!(is_alpha(buf[i]) || is_digit(buf[i]))) {
      return false;
    }
  }

  return true;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_uri_node(SerdWriter* const        writer,
               const SerdNode*          node,
               const SerdField          field,
               const SerdStatementFlags flags)
{
  SerdStatus st = SERD_SUCCESS;

  if (is_inline_start(writer, field, flags)) {
    TRY(st, write_sep(writer, flags, SEP_ANON_BEGIN));
    TRY(st, esink(" == ", 4, writer));
  }

  const SerdNode* prefix     = NULL;
  SerdStringView  suffix     = {NULL, 0};
  const char*     node_str   = serd_node_string(node);
  const bool      has_scheme = serd_uri_string_has_scheme(node_str);
  if (supports_abbrev(writer)) {
    if (field == SERD_PREDICATE &&
        serd_node_equals(node, writer->world->rdf_type)) {
      return esink("a", 1, writer);
    }

    if (serd_node_equals(node, writer->world->rdf_type)) {
      return esink("()", 2, writer);
    }

    if (has_scheme && !(writer->flags & SERD_WRITE_UNQUALIFIED) &&
        serd_env_qualify_in_place(writer->env, node, &prefix, &suffix) &&
        is_name(serd_node_string(prefix), serd_node_length(prefix)) &&
        is_name(suffix.buf, suffix.len)) {
      TRY(st, write_uri_from_node(writer, prefix));
      TRY(st, esink(":", 1, writer));
      return ewrite_uri(writer, suffix.buf, suffix.len);
    }
  }

  if (!has_scheme && !supports_uriref(writer) &&
      !serd_env_base_uri(writer->env)) {
    serd_world_errorf(writer->world,
                      SERD_ERR_BAD_ARG,
                      "syntax does not support URI reference <%s>\n",
                      node_str);
    return SERD_ERR_BAD_ARG;
  }

  TRY(st, esink("<", 1, writer));
  if (!(writer->flags & SERD_WRITE_UNRESOLVED) &&
      serd_env_base_uri(writer->env)) {
    const SerdURIView  base_uri = serd_env_base_uri_view(writer->env);
    SerdURIView        uri      = serd_parse_uri(node_str);
    SerdURIView        abs_uri  = serd_resolve_uri(uri, base_uri);
    bool               rooted   = uri_is_under(&base_uri, &writer->root_uri);
    const SerdURIView* root     = rooted ? &writer->root_uri : &base_uri;
    UriSinkContext     ctx      = {writer, SERD_SUCCESS};
    const bool         write_abs =
      (!supports_abbrev(writer) || !uri_is_under(&abs_uri, root));

    write_abs
      ? serd_write_uri(abs_uri, uri_sink, &ctx)
      : serd_write_uri(serd_relative_uri(uri, base_uri), uri_sink, &ctx);

    st = ctx.status;
    if (st && !(writer->flags & SERD_WRITE_LAX)) {
      return st;
    }
  } else {
    TRY(st, write_uri_from_node(writer, node));
  }
  TRY(st, esink(">", 1, writer));

  return is_inline_start(writer, field, flags) ? esink(" ;", 2, writer) : st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_curie(SerdWriter* const        writer,
            const SerdNode*          node,
            const SerdField          field,
            const SerdStatementFlags flags)
{
  writer->last_sep = SEP_NONE;

  SerdStringView prefix = {NULL, 0};
  SerdStringView suffix = {NULL, 0};
  SerdStatus     st     = SERD_SUCCESS;
  switch (writer->syntax) {
  case SERD_NTRIPLES:
  case SERD_NQUADS:
    if ((st = serd_env_expand_in_place(writer->env, node, &prefix, &suffix))) {
      serd_world_errorf(writer->world,
                        st,
                        "undefined namespace prefix `%s'\n",
                        serd_node_string(node));
      return st;
    }
    TRY(st, esink("<", 1, writer));
    TRY(st, ewrite_uri(writer, prefix.buf, prefix.len));
    TRY(st, ewrite_uri(writer, suffix.buf, suffix.len));
    TRY(st, esink(">", 1, writer));
    break;
  case SERD_TURTLE:
  case SERD_TRIG:
    if (is_inline_start(writer, field, flags)) {
      TRY(st, write_sep(writer, flags, SEP_ANON_BEGIN));
      TRY(st, esink(" == ", 4, writer));
    }
    TRY(st, write_lname(writer, serd_node_string(node), node->n_bytes));
    if (is_inline_start(writer, field, flags)) {
      TRY(st, esink(" ;", 2, writer));
    }
  case SERD_SYNTAX_EMPTY:
    break;
  }
  return st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_blank(SerdWriter* const        writer,
            const SerdNode*          node,
            const SerdField          field,
            const SerdStatementFlags flags)
{
  const char* node_str = serd_node_string(node);
  if (supports_abbrev(writer)) {
    if (is_inline_start(writer, field, flags)) {
      return write_sep(writer, flags, SEP_ANON_BEGIN);
    }

    if ((field == SERD_SUBJECT && (flags & SERD_LIST_S)) ||
        (field == SERD_OBJECT && (flags & SERD_LIST_O))) {
      return write_sep(writer, flags, SEP_LIST_BEGIN);
    }

    if (field == SERD_SUBJECT && (flags & SERD_EMPTY_S)) {
      writer->last_sep = SEP_NONE; // Treat "[]" like a node
      return esink("[]", 2, writer);
    }
  }

  SerdStatus st = esink("_:", 2, writer);
  if (!st && writer->bprefix &&
      !strncmp(node_str, writer->bprefix, writer->bprefix_len)) {
    TRY(st,
        esink(node_str + writer->bprefix_len,
              node->n_bytes - writer->bprefix_len,
              writer));
  } else {
    TRY(st, esink(node_str, node->n_bytes, writer));
  }

  writer->last_sep = SEP_NONE;
  return st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_variable(SerdWriter* const writer, const SerdNode* node)
{
  SerdStatus st = SERD_SUCCESS;

  TRY(st, esink("?", 1, writer));
  TRY(st, esink(serd_node_string(node), node->n_bytes, writer));

  writer->last_sep = SEP_NONE;
  return st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_node(SerdWriter*        writer,
           const SerdNode*    node,
           const SerdField    field,
           SerdStatementFlags flags)
{
  switch (node->type) {
  case SERD_LITERAL:
    return write_literal(writer, node, flags);
  case SERD_URI:
    return write_uri_node(writer, node, field, flags);
  case SERD_CURIE:
    return write_curie(writer, node, field, flags);
  case SERD_BLANK:
    return write_blank(writer, node, field, flags);
  case SERD_VARIABLE:
    return write_variable(writer, node);
  }

  return SERD_ERR_INTERNAL;
}

static inline bool
is_resource(const SerdNode* node)
{
  return node && node->type > SERD_LITERAL;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_pred(SerdWriter* writer, SerdStatementFlags flags, const SerdNode* pred)
{
  SerdStatus st = SERD_SUCCESS;
  TRY(st, write_node(writer, pred, SERD_PREDICATE, flags));
  TRY(st, write_sep(writer, flags, SEP_P_O));
  serd_node_set(&writer->context.predicate, pred);
  return st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
write_list_obj(SerdWriter*        writer,
               SerdStatementFlags flags,
               const SerdNode*    predicate,
               const SerdNode*    object,
               bool*              is_end)
{
  if (serd_node_equals(object, writer->world->rdf_nil)) {
    *is_end = true;
    return write_sep(writer, writer->context.flags, SEP_LIST_END);
  }

  return (serd_node_equals(predicate, writer->world->rdf_first)
            ? write_node(writer, object, SERD_OBJECT, flags)
            : write_sep(writer, writer->context.flags, SEP_LIST_SEP));
}

static SerdStatus
serd_writer_write_statement(SerdWriter*          writer,
                            SerdStatementFlags   flags,
                            const SerdStatement* statement)
{
  assert(!((flags & SERD_ANON_S) && (flags & SERD_LIST_S)));
  assert(!((flags & SERD_ANON_O) && (flags & SERD_LIST_O)));

  if (writer->syntax == SERD_SYNTAX_EMPTY) {
    return SERD_SUCCESS;
  }

  SerdStatus            st        = SERD_SUCCESS;
  const SerdNode* const subject   = serd_statement_subject(statement);
  const SerdNode* const predicate = serd_statement_predicate(statement);
  const SerdNode* const object    = serd_statement_object(statement);
  const SerdNode* const graph     = serd_statement_graph(statement);

  if (!is_resource(subject) || !is_resource(predicate) || !object ||
      ((flags & SERD_ANON_S) && (flags & SERD_LIST_S)) ||  // Nonsense
      ((flags & SERD_ANON_O) && (flags & SERD_LIST_O)) ||  // Nonsense
      ((flags & SERD_ANON_S) && (flags & SERD_TERSE_S)) || // Unsupported
      ((flags & SERD_ANON_O) && (flags & SERD_TERSE_O))) { // Unsupported
    return SERD_ERR_BAD_ARG;
  }

  if (writer->syntax == SERD_NTRIPLES || writer->syntax == SERD_NQUADS) {
    TRY(st, write_node(writer, subject, SERD_SUBJECT, flags));
    TRY(st, esink(" ", 1, writer));
    TRY(st, write_node(writer, predicate, SERD_PREDICATE, flags));
    TRY(st, esink(" ", 1, writer));
    TRY(st, write_node(writer, object, SERD_OBJECT, flags));
    if (writer->syntax == SERD_NQUADS && graph) {
      TRY(st, esink(" ", 1, writer));
      TRY(st, write_node(writer, graph, SERD_GRAPH, flags));
    }
    TRY(st, esink(" .\n", 3, writer));
    return SERD_SUCCESS;
  }

  if ((graph && !serd_node_equals(graph, writer->context.graph)) ||
      (!graph && ctx(writer, SERD_GRAPH))) {
    if (ctx(writer, SERD_SUBJECT)) {
      TRY(st, write_sep(writer, writer->context.flags, SEP_END_S));
    }

    if (ctx(writer, SERD_GRAPH)) {
      TRY(st, write_sep(writer, writer->context.flags, SEP_GRAPH_END));
    }

    TRY(st, write_top_level_sep(writer));
    reset_context(writer, true);

    if (graph) {
      TRY(st, write_node(writer, graph, SERD_GRAPH, flags));
      TRY(st, write_sep(writer, flags, SEP_GRAPH_BEGIN));
      serd_node_set(&writer->context.graph, graph);
    }
  }

  if (writer->context.type == CTX_LIST) {
    bool is_end = false;
    TRY(st, write_list_obj(writer, flags, predicate, object, &is_end));
    if (is_end) {
      // Reached end of list
      pop_context(writer);
      return SERD_SUCCESS;
    }
  } else if (serd_node_equals(subject, writer->context.subject)) {
    if (serd_node_equals(predicate, writer->context.predicate)) {
      // Abbreviate S P
      if (!writer->context.indented_object &&
          !(flags & (SERD_ANON_O | SERD_LIST_O))) {
        ++writer->indent;
        writer->context.indented_object = true;
      }

      TRY(st, write_sep(writer, writer->context.flags, SEP_END_O));
      TRY(st, write_node(writer, object, SERD_OBJECT, flags));
    } else {
      // Abbreviate S
      if (writer->context.indented_object && writer->indent > 0) {
        --writer->indent;
        writer->context.indented_object = false;
      }

      const Sep sep = ctx(writer, SERD_PREDICATE) ? SEP_END_P : SEP_S_P;
      TRY(st, write_sep(writer, writer->context.flags, sep));
      TRY(st, write_pred(writer, writer->context.flags, predicate));
      TRY(st, write_node(writer, object, SERD_OBJECT, flags));
    }
  } else {
    // No abbreviation
    if (writer->context.indented_object && writer->indent > 0) {
      --writer->indent;
      writer->context.indented_object = false;
    }

    if (writer->anon_stack_size == 0) {
      if (ctx(writer, SERD_SUBJECT)) { // Terminate last subject
        TRY(st, write_sep(writer, writer->context.flags, SEP_END_S));
      }
      TRY(st, write_top_level_sep(writer));
    }

    if (writer->anon_stack_size == 0) {
      TRY(st, write_node(writer, subject, SERD_SUBJECT, flags));
      if (!(flags & (SERD_ANON_S | SERD_LIST_S))) {
        TRY(st, write_sep(writer, writer->context.flags, SEP_S_P));
      } else if (flags & SERD_ANON_S) {
        TRY(st, write_sep(writer, writer->context.flags, SEP_ANON_S_P));
      }
    } else {
      TRY(st, write_sep(writer, writer->context.flags, SEP_ANON_S_P));
    }

    reset_context(writer, false);
    serd_node_set(&writer->context.subject, subject);

    if (!(flags & SERD_LIST_S)) {
      TRY(st, write_pred(writer, flags, predicate));
    }

    TRY(st, write_node(writer, object, SERD_OBJECT, flags));
  }

  // Push context for list or anonymous subject if necessary
  if (!st) {
    if (flags & SERD_ANON_S) {
      st = push_context(writer, CTX_BLANK, flags, graph, subject, predicate);
    } else if (flags & SERD_LIST_S) {
      st = push_context(writer, CTX_LIST, flags, graph, subject, NULL);
    }
  }

  // Push context for list or anonymous object if necessary
  if (!st) {
    if (flags & SERD_ANON_O) {
      st = push_context(writer, CTX_BLANK, flags, graph, object, NULL);
    } else if (flags & SERD_LIST_O) {
      st = push_context(writer, CTX_LIST, flags, graph, object, NULL);
    }
  }

  // Update current context to this statement if this isn't a new context
  if (!st) {
    if (!(flags & (SERD_ANON_S | SERD_LIST_S | SERD_ANON_O | SERD_LIST_O))) {
      serd_node_set(&writer->context.graph, graph);
      serd_node_set(&writer->context.subject, subject);
      serd_node_set(&writer->context.predicate, predicate);
    }
  }

  return st;
}

SERD_WARN_UNUSED_RESULT static SerdStatus
serd_writer_end_anon(SerdWriter* writer, const SerdNode* node)
{
  if (writer->syntax != SERD_TURTLE && writer->syntax != SERD_TRIG) {
    return SERD_SUCCESS;
  }

  if (writer->anon_stack_size == 0) {
    return serd_world_errorf(writer->world,
                             SERD_ERR_UNKNOWN,
                             "unexpected end of anonymous node `%s'\n",
                             serd_node_string(node));
  }

  SerdStatus st = write_sep(writer, writer->context.flags, SEP_ANON_END);
  pop_context(writer);

  if (writer->context.predicate &&
      serd_node_equals(node, writer->context.subject)) {
    // Now-finished anonymous node is the new subject with no other context
    memset(writer->context.predicate, 0, sizeof(SerdNode));
  }

  return st;
}

static SerdStatus
serd_writer_on_event(SerdWriter* writer, const SerdEvent* event)
{
  switch (event->type) {
  case SERD_BASE:
    return serd_writer_set_base_uri(writer, event->base.uri);
  case SERD_PREFIX:
    return serd_writer_set_prefix(
      writer, event->prefix.name, event->prefix.uri);
  case SERD_STATEMENT:
    return serd_writer_write_statement(
      writer, event->statement.flags, event->statement.statement);
  case SERD_END:
    return serd_writer_end_anon(writer, event->end.node);
  }

  return SERD_SUCCESS;
}

SerdStatus
serd_writer_finish(SerdWriter* writer)
{
  SerdStatus st = SERD_SUCCESS;
  if (ctx(writer, SERD_SUBJECT)) {
    st = write_sep(writer, writer->context.flags, SEP_END_S);
  }

  if (!st && ctx(writer, SERD_GRAPH)) {
    st = write_sep(writer, writer->context.flags, SEP_GRAPH_END);
  }

  // Free any lingering contexts in case there was an error
  while (writer->anon_stack_size > 0) {
    pop_context(writer);
  }

  free_context(writer);
  writer->indent  = 0;
  writer->context = WRITE_CONTEXT_NULL;
  writer->empty   = true;
  return st;
}

SerdWriter*
serd_writer_new(SerdWorld*      world,
                SerdSyntax      syntax,
                SerdWriterFlags flags,
                SerdEnv*        env,
                SerdByteSink*   byte_sink)
{
  const WriteContext context = WRITE_CONTEXT_NULL;
  SerdWriter*        writer  = (SerdWriter*)calloc(1, sizeof(SerdWriter));

  writer->world     = world;
  writer->syntax    = syntax;
  writer->flags     = flags;
  writer->env       = env;
  writer->root_node = NULL;
  writer->root_uri  = SERD_URI_NULL;
  writer->anon_stack =
    (WriteContext*)calloc(anon_stack_capacity, sizeof(WriteContext));
  writer->byte_sink = byte_sink;
  writer->context   = context;
  writer->empty     = true;

  writer->iface.handle   = writer;
  writer->iface.on_event = (SerdEventFunc)serd_writer_on_event;

  return writer;
}

void
serd_writer_chop_blank_prefix(SerdWriter* writer, const char* prefix)
{
  free(writer->bprefix);
  writer->bprefix_len = 0;
  writer->bprefix     = NULL;

  const size_t prefix_len = prefix ? strlen(prefix) : 0;
  if (prefix_len) {
    writer->bprefix_len = prefix_len;
    writer->bprefix     = (char*)malloc(writer->bprefix_len + 1);
    memcpy(writer->bprefix, prefix, writer->bprefix_len + 1);
  }
}

SerdStatus
serd_writer_set_base_uri(SerdWriter* writer, const SerdNode* uri)
{
  if (uri->type != SERD_URI) {
    return SERD_ERR_BAD_ARG;
  }

  SerdStatus st =
    serd_env_set_base_uri(writer->env, serd_node_string_view(uri));

  if (!st) {
    if (writer->syntax == SERD_TURTLE || writer->syntax == SERD_TRIG) {
      if (ctx(writer, SERD_GRAPH) || ctx(writer, SERD_SUBJECT)) {
        TRY(st, esink(" .\n\n", 4, writer));
        reset_context(writer, true);
      }
      TRY(st, esink("@base <", 7, writer));
      TRY(st, esink(serd_node_string(uri), uri->n_bytes, writer));
      TRY(st, esink("> .\n", 4, writer));
    }
    writer->indent = 0;
    reset_context(writer, true);
  }

  return st;
}

SerdStatus
serd_writer_set_root_uri(SerdWriter* writer, const SerdNode* uri)
{
  serd_node_free(writer->root_node);
  if (uri) {
    writer->root_node = serd_node_copy(uri);
    writer->root_uri  = serd_node_uri_view(writer->root_node);
  } else {
    writer->root_node = NULL;
    writer->root_uri  = SERD_URI_NULL;
  }
  return SERD_SUCCESS;
}

SerdStatus
serd_writer_set_prefix(SerdWriter*     writer,
                       const SerdNode* name,
                       const SerdNode* uri)
{
  if (name->type != SERD_LITERAL || uri->type != SERD_URI) {
    return SERD_ERR_BAD_ARG;
  }

  SerdStatus st = serd_env_set_prefix(
    writer->env, serd_node_string_view(name), serd_node_string_view(uri));

  if (!st) {
    if (writer->syntax == SERD_TURTLE || writer->syntax == SERD_TRIG) {
      if (ctx(writer, SERD_GRAPH) || ctx(writer, SERD_SUBJECT)) {
        TRY(st, esink(" .\n\n", 4, writer));
        reset_context(writer, true);
      }

      TRY(st, esink("@prefix ", 8, writer));
      TRY(st, esink(serd_node_string(name), name->n_bytes, writer));
      TRY(st, esink(": <", 3, writer));
      TRY(st, write_uri_from_node(writer, uri));
      TRY(st, esink("> .\n", 4, writer));
    }

    writer->indent = 0;
    reset_context(writer, true);
  }

  return st;
}

void
serd_writer_free(SerdWriter* writer)
{
  if (!writer) {
    return;
  }

  serd_writer_finish(writer);
  free(writer->anon_stack);
  free(writer->bprefix);
  serd_node_free(writer->root_node);
  free(writer);
}

const SerdSink*
serd_writer_sink(SerdWriter* writer)
{
  return &writer->iface;
}

SerdEnv*
serd_writer_env(SerdWriter* writer)
{
  return writer->env;
}

size_t
serd_buffer_sink(const void* buf, size_t size, size_t nmemb, void* stream)
{
  assert(size == 1);
  (void)size;

  SerdBuffer* buffer = (SerdBuffer*)stream;
  buffer->buf        = (char*)realloc(buffer->buf, buffer->len + nmemb);
  memcpy((uint8_t*)buffer->buf + buffer->len, buf, nmemb);
  buffer->len += nmemb;
  return nmemb;
}

char*
serd_buffer_sink_finish(SerdBuffer* stream)
{
  serd_buffer_sink("", 1, 1, stream);
  return (char*)stream->buf;
}