an_editor/src/buffer.h

#ifndef ED_BUFFER_INCLUDED
#define ED_BUFFER_INCLUDED
#include "ed_array.h"
#include "string.h"
#include "ui.h"
#include <stdbool.h>

typedef struct {
    size_t link_index;
    size_t content_index;
} ed_buffer_offset;

typedef struct {
    uint64_t column;
    uint64_t line;
    ed_buffer_offset offset;
} ed_buffer_cursor;

typedef enum {
    ED_BUFFER_CONTENT_LINK_TYPE_ORIGINAL,
    ED_BUFFER_CONTENT_LINK_TYPE_ADDED,
} ed_buffer_content_link_t;

typedef struct {
    ed_buffer_content_link_t type;
    size_t start;
    size_t end;
    size_t len;
} ed_buffer_content_link;
arrayTemplate(ed_buffer_content_link);

typedef struct {
    array(uint8_t) original_content;
    array(uint8_t) added_content;

    array(ed_buffer_content_link) linked_content;
} ed_buffer_data;

typedef struct {
    ed_buffer_data data;
    ed_buffer_cursor cursor;
} ed_buffer;

#ifdef ED_BUFFER_IMPLEMENTATION

static ed_buffer_data _ed_buffer_init_buffer_data(slice(uint8_t) data) {
    array(ed_buffer_content_link) linked_content = newArray(ed_buffer_content_link, 16);
    pushArray(ed_buffer_content_link, &linked_content, ((ed_buffer_content_link) {
        .type = ED_BUFFER_CONTENT_LINK_TYPE_ORIGINAL,
        .start = 0,
        .end = data.len,
        .len = data.len,
    }));

    return (ed_buffer_data) {
        .original_content = newArrayFromSlice(uint8_t, data),
        .added_content = newArray(uint8_t, 512),
        .linked_content = linked_content,
    };
}

uint8_t ed_buffer_get_char_at(ed_buffer *buffer, ed_buffer_cursor cursor) {
    ed_buffer_content_link link = buffer->data.linked_content.data[cursor.offset.link_index];
    uint8_t character;

    if (link.type == ED_BUFFER_CONTENT_LINK_TYPE_ORIGINAL) {
        character = buffer->data.original_content.data[link.start+cursor.offset.content_index];
    } else if (link.type == ED_BUFFER_CONTENT_LINK_TYPE_ADDED) {
        character = buffer->data.added_content.data[link.start+cursor.offset.content_index];
    } else {
        character = 0;
    }

    return character;
}

ed_buffer ed_buffer_from_file(string path) {
    char text[] = 
"bool ht_set(ed_ht *ht, string key, void *value) {\n"
"    ht_hash_t hash = ht_hash(key, ht->capacity);\n"
"\n"
"    for (size_t i=hash; i<ht->capacity; ++i) {\n"
"        if (ht->key_slots[i].key.data == NULL || string_eq(ht->key_slots[i].key, key)) {\n"
"            if (ht->key_slots[i].key.data != NULL) {\n"
"                free(ht->key_slots[i].key.data);\n"
"            }\n"
"            ht->key_slots[i].key = string_copy(key);\n"
"\n"
"            memcpy(ht->value_slots+i*ht->value_size, value, ht->value_size);\n"
"            return true;\n"
"        }\n"
"    }\n"
"    return false;\n"
"}\n";

    slice(uint8_t) data = {
        .data = text,
        .len = sizeof(text),
    };
    ed_buffer buffer = {
        .data = _ed_buffer_init_buffer_data(data),
        .cursor = {
            .column = 0,
            .line = 0,
            .offset = {
                .link_index = 0,
                .content_index = 0,
            },
        }
    };

    return buffer;
}

bool ed_buffer_content_iter(ed_buffer *buffer, ed_buffer_cursor *cursor) {
    if (cursor->offset.link_index >= buffer->data.linked_content.size
            || cursor->offset.content_index >= (buffer->data.linked_content.data[cursor->offset.link_index].len))
    {
        return false;
    }

    uint8_t character = ed_buffer_get_char_at(buffer, *cursor);

    ed_buffer_content_link link = buffer->data.linked_content.data[cursor->offset.link_index];
    if (cursor->offset.content_index < link.len-1) {
        cursor->offset.content_index += 1;
    } else if (cursor->offset.link_index < buffer->data.linked_content.size-1) {
        cursor->offset.content_index = 0;
        cursor->offset.link_index += 1;
    } else {
        return false;
    }

    if (character == '\n') {
        cursor->column = 0;
        cursor->line += 1;
    } else {
        cursor->column += 1;
    }

    return true;
}

void ed_buffer_insert_text(ed_buffer *buffer, string text, ed_buffer_cursor cursor) {
    if (text.len == 0) {
        return;
    }  

    size_t content_start = buffer->data.added_content.size;
    pushArrayMulti(uint8_t, &buffer->data.added_content, text.data, text.len);

    if (cursor.offset.content_index == 0) {
        insertArrayAt(ed_buffer_content_link,
            &buffer->data.linked_content,
            cursor.offset.link_index,
            ((ed_buffer_content_link) {
                .type = ED_BUFFER_CONTENT_LINK_TYPE_ADDED,
                .start = content_start,
                .end = content_start+text.len,
                .len = text.len,
            })
        );
    } else {
        ed_buffer_content_link end_link = buffer->data.linked_content.data[cursor.offset.link_index];
        end_link.start += cursor.offset.content_index;
        end_link.len -= cursor.offset.content_index;

        buffer->data.linked_content.data[cursor.offset.link_index].end = end_link.start;
        buffer->data.linked_content.data[cursor.offset.link_index].len = buffer->data.linked_content.data[cursor.offset.link_index].end - buffer->data.linked_content.data[cursor.offset.link_index].start;

        // insert new content
        insertArrayAt(ed_buffer_content_link,
            &buffer->data.linked_content,
            cursor.offset.link_index+1,
            ((ed_buffer_content_link) {
                .type = ED_BUFFER_CONTENT_LINK_TYPE_ADDED,
                .start = content_start,
                .end = content_start+text.len,
                .len = text.len,
            })
        );
        
        // insert cut slice
        insertArrayAt(ed_buffer_content_link,
            &buffer->data.linked_content,
            cursor.offset.link_index+2,
            end_link
        );
    }
}

void ed_buffer_render(ui_context *cx, ed_buffer *buffer) {
    ui_element(cx, _String("Buffer"), UI_AXIS_VERTICAL, ui_make_size(ui_fill, ui_fill), UI_FLAG_DRAW_BACKGROUND);
    ui_push_parent(cx);
    {
        ed_buffer_cursor cursor = buffer->cursor;
        do {
            uint8_t line_buffer[512];
            size_t line_buffer_index = 0;

            do {
                uint8_t character = ed_buffer_get_char_at(buffer, cursor);
                if (character == '\n' || line_buffer_index >= 512) {
                    break;
                }

                line_buffer[line_buffer_index] = character;
                line_buffer_index += 1;
            } while(ed_buffer_content_iter(buffer, &cursor));

            uint8_t *str = malloc(line_buffer_index * sizeof(uint8_t));
            memcpy(str, line_buffer, line_buffer_index * sizeof(uint8_t));

            ui_element(cx,
                (string){ .data = str,
                    .len = line_buffer_index,
                    .owned = true
                },
                UI_AXIS_HORIZONTAL,
                ui_make_size(ui_fit_text, ui_fit_text),
                UI_FLAG_DRAW_TEXT|UI_FLAG_DRAW_BACKGROUND
            );
        } while(ed_buffer_content_iter(buffer, &cursor));
    }
    ui_pop_parent(cx);
}

#endif
#endif