#include "../graph/graph_internal.h"
#include "project_internal.h"
#include <stdlib.h>
#include <string.h>

struct xtc_history {
    xtc_project *states[XTC_HISTORY_EDITS + 1];
    size_t count, cursor;
    xtc_project *reserved;
    uint64_t next_track, next_clip, next_note;
    size_t next_node;
};

/**
 * @brief Raises history's identifier high-water marks to include the project's allocations.
 *
 * @param h Snapshot history handle.
 * @param p Project model; borrowed for this call.
 */
static void remember_ids(xtc_history *h, const xtc_project *p)
{
    if (p->next_track_id > h->next_track)
        h->next_track = p->next_track_id;
    if (p->next_clip_id > h->next_clip)
        h->next_clip = p->next_clip_id;
    if (p->next_note_id > h->next_note)
        h->next_note = p->next_note_id;
    if (p->graph->next_id > h->next_node)
        h->next_node = p->graph->next_id;
}

/**
 * @brief Releases all retained snapshots and history storage; accepts NULL.
 *
 * @param h Snapshot history handle.
 */
void xtc_history_destroy(xtc_history *h)
{
    size_t i;
    if (!h)
        return;
    for (i = 0; i < h->count; ++i)
        xtc_project_destroy(h->states[i]);
    xtc_project_destroy(h->reserved);
    free(h);
}

/**
 * @brief Creates snapshot history with an independent copy of the initial project.
 *
 * @param p Project model; borrowed for this call.
 * @param out Receives the newly allocated object; caller owns it on success.
 * @return XTC_OK on success, or an error code describing the failure.
 */
xtc_result xtc_history_create(const xtc_project *p, xtc_history **out)
{
    xtc_history *h;
    xtc_result r;
    if (!out)
        return XTC_ERR_INVALID_ARGUMENT;
    *out = NULL;
    if (!p)
        return XTC_ERR_INVALID_ARGUMENT;
    h = calloc(1, sizeof(*h));
    if (!h)
        return XTC_ERR_OUT_OF_MEMORY;
    r = xtc_project_clone(p, h->states);
    if (r != XTC_OK) {
        free(h);
        return r;
    }
    remember_ids(h, p);
    h->count = 1;
    *out = h;
    return XTC_OK;
}

xtc_result xtc_history_reserve(xtc_history *h)
{
    if (!h) return XTC_ERR_INVALID_ARGUMENT;
    if (h->reserved) return XTC_OK;
    return xtc_project_create(&h->reserved);
}
xtc_result xtc_history_counts(const xtc_history *h, size_t *undo_count, size_t *redo_count)
{
    if (!h || !undo_count || !redo_count || undo_count == redo_count) return XTC_ERR_INVALID_ARGUMENT;
    *undo_count = h->cursor;
    *redo_count = h->count-h->cursor-1;
    return XTC_OK;
}
/* Copy into the preallocated project and 64-node/4096-edge graph. No allocation
 * can fail after an accepted model command or successful engine publication. */
static xtc_result capture(xtc_history *h, const xtc_project *p, xtc_project **out)
{
    xtc_project *copy = h->reserved;
    xtc_graph *graph;
    xtc_node *nodes;
    xtc_edge *edges;
    if (!copy) return xtc_project_clone(p,out);
    if (p->graph->node_count > 64 || p->graph->edge_count > 4096) return XTC_ERR_CAPACITY;
    graph = copy->graph; nodes = graph->nodes; edges = graph->edges;
    *copy = *p;
    copy->graph = graph;
    *graph = *p->graph;
    graph->max_nodes = 64; graph->nodes = nodes; graph->edges = edges;
    memcpy(nodes,p->graph->nodes,p->graph->node_count*sizeof(*nodes));
    memcpy(edges,p->graph->edges,p->graph->edge_count*sizeof(*edges));
    h->reserved = NULL;
    *out = copy;
    return XTC_OK;
}

/**
 * @brief Appends a project snapshot, discarding redo states and evicting the oldest state if full.
 *
 * @param h Snapshot history handle.
 * @param p Project model; borrowed for this call.
 * @return XTC_OK on success, or an error code describing the failure.
 */
xtc_result xtc_history_record(xtc_history *h, const xtc_project *p)
{
    xtc_project *copy;
    size_t i;
    xtc_result r;
    if (!h || !p)
        return XTC_ERR_INVALID_ARGUMENT;
    r = capture(h,p,&copy);
    if (r != XTC_OK)
        return r;
    remember_ids(h, p);
    for (i = h->cursor + 1; i < h->count; ++i)
        xtc_project_destroy(h->states[i]);
    h->count = h->cursor + 1;
    if (h->count == XTC_HISTORY_EDITS + 1) {
        xtc_project_destroy(h->states[0]);
        memmove(h->states, h->states + 1, XTC_HISTORY_EDITS * sizeof(*h->states));
        --h->count;
    }
    h->states[h->count++] = copy;
    h->cursor = h->count - 1;
    return XTC_OK;
}

/**
 * @brief Checks whether an adjacent undo or redo snapshot exists.
 *
 * @param h Snapshot history handle.
 * @param redo Zero for undo, one for redo.
 * @return Nonzero when the requested history state exists, zero otherwise.
 */
static int available(const xtc_history *h, int redo)
{
    return redo ? h->cursor + 1 < h->count : h->cursor > 0;
}

/**
 * @brief Clones the adjacent undo or redo state without moving the history cursor.
 *
 * @param h Snapshot history handle.
 * @param redo Zero for undo, one for redo.
 * @param out Receives the newly allocated object; caller owns it on success.
 * @return XTC_OK on success, or an error code describing the failure.
 */
xtc_result xtc_history_checkout(const xtc_history *h, int redo, xtc_project **out)
{
    if (!out)
        return XTC_ERR_INVALID_ARGUMENT;
    *out = NULL;
    if (!h || (redo != 0 && redo != 1))
        return XTC_ERR_INVALID_ARGUMENT;
    if (!available(h, redo))
        return XTC_ERR_NOT_FOUND;
    {
        xtc_result r = xtc_project_clone(h->states[redo ? h->cursor + 1 : h->cursor - 1], out);
        if (r == XTC_OK) {
            (*out)->next_track_id = h->next_track;
            (*out)->next_clip_id = h->next_clip;
            (*out)->next_note_id = h->next_note;
            (*out)->graph->next_id = h->next_node;
        }
        return r;
    }
}

/**
 * @brief Moves the history cursor after the checked-out project has been installed.
 *
 * @param h Snapshot history handle.
 * @param redo Zero for undo, one for redo.
 * @return XTC_OK on success, or an error code describing the failure.
 */
xtc_result xtc_history_accept(xtc_history *h, int redo)
{
    if (!h || (redo != 0 && redo != 1))
        return XTC_ERR_INVALID_ARGUMENT;
    if (!available(h, redo))
        return XTC_ERR_NOT_FOUND;
    if (redo)
        ++h->cursor;
    else
        --h->cursor;
    return XTC_OK;
}