package proposals

import (
	"strings"

	"gitea.maximumdirect.net/eric/audita/internal/core/schema"
)

// ProposalSkipReason is a stable, report-friendly reason code for
// unapplied/unsafe proposals.
type ProposalSkipReason string

const (
	SkipReasonMissingSegment      ProposalSkipReason = "missing_segment"
	SkipReasonMissingOriginalText ProposalSkipReason = "missing_original_text"
	SkipReasonAmbiguousOriginal   ProposalSkipReason = "ambiguous_original_text"
	SkipReasonNoEffect            ProposalSkipReason = "no_effect"
	SkipReasonInvalidProposal     ProposalSkipReason = "invalid_proposal"
)

// SegmentPreviewResult is a deterministic preview of applying one proposal to
// one transcript segment.
type SegmentPreviewResult struct {
	Applicable           bool               `json:"applicable"`
	CorrectedSegmentText string             `json:"corrected_segment_text,omitempty"`
	ReplacementCount     int                `json:"replacement_count"`
	SkipReason           ProposalSkipReason `json:"skip_reason,omitempty"`
}

// PreviewProposalForSegment previews applying a proposal to a single segment
// under the given replacement policy without mutating the input segment.
func PreviewProposalForSegment(segment *schema.Segment, proposal CorrectionProposal, policy ReplacementPolicy) SegmentPreviewResult {
	if segment == nil {
		return SegmentPreviewResult{SkipReason: SkipReasonMissingSegment}
	}

	if err := proposal.Validate(); err != nil {
		return SegmentPreviewResult{SkipReason: SkipReasonInvalidProposal}
	}

	if !policy.IsValid() {
		return SegmentPreviewResult{SkipReason: SkipReasonInvalidProposal}
	}

	if proposal.TargetSegmentID != segment.ID {
		return SegmentPreviewResult{SkipReason: SkipReasonMissingSegment}
	}

	matchCount := strings.Count(segment.Text, proposal.OriginalText)
	if matchCount == 0 {
		return SegmentPreviewResult{SkipReason: SkipReasonMissingOriginalText}
	}

	if proposal.OriginalText == proposal.CorrectedText {
		return SegmentPreviewResult{SkipReason: SkipReasonNoEffect}
	}

	switch policy {
	case ReplacementPolicyRequireUnique:
		if matchCount != 1 {
			return SegmentPreviewResult{SkipReason: SkipReasonAmbiguousOriginal}
		}

		corrected := strings.Replace(segment.Text, proposal.OriginalText, proposal.CorrectedText, 1)
		return SegmentPreviewResult{
			Applicable:           true,
			CorrectedSegmentText: corrected,
			ReplacementCount:     1,
		}

	case ReplacementPolicyReplaceAll:
		corrected := strings.ReplaceAll(segment.Text, proposal.OriginalText, proposal.CorrectedText)
		return SegmentPreviewResult{
			Applicable:           true,
			CorrectedSegmentText: corrected,
			ReplacementCount:     matchCount,
		}
	}

	return SegmentPreviewResult{SkipReason: SkipReasonInvalidProposal}
}