#!/bin/bash
# ==============================================================================================
# ================================= DECISION ENGINE ============================================
# ==============================================================================================
# Central behavior-driven decision kernel used by media automation systems.
#
# This engine does NOT download media.
# This engine does NOT search indexers.
# This engine does NOT manage applications directly.
#
# Instead:
#   It evaluates candidates.
#   Scores them against ecosystem behavior.
#   Applies adaptive filtering rules.
#   Returns decisions to consumer scripts.
#
# ==============================================================================================
# ── DESIGN PHILOSOPHY ─────────────────────────────────────────────────────────────────────────
#
# The ecosystem is built around:
#
#   Family-aware decisions
#   Time-aware weighting
#   Behavior-driven adaptation
#   Domain-specific strictness
#
# Each media domain consumes the engine differently:
#
#   Lidarr  → highly selective, quality-first discovery
#   Sonarr  → balanced family-aware episodic intake
#   Radarr  → broader flexibility with intelligent filtering
#
# The engine itself remains domain-agnostic.
# Consumers define their own thresholds, weights, and strictness profiles.
#
# This separation prevents:
#
#   Cross-domain bias pollution
#   Unified-feed degeneration
#   Overfitting to a single user's habits
#   Low-quality recommendation drift over time
#
# Result:
#
#   Music stays curated and intentional
#   TV stays balanced across users
#   Movies remain adaptive without chaos
#
# ==============================================================================================
# ── RESPONSIBILITIES ──────────────────────────────────────────────────────────────────────────
#
# The decision engine is responsible for:
#
#   Candidate scoring
#   User weighting
#   Temporal decay
#   Popularity normalization
#   Duplicate prevention
#   Strictness enforcement
#   Threshold evaluation
#   Final decision output
#
# The engine returns:
#
#   ACCEPT
#   REJECT
#   SCORE
#   REASON
#
# Consumer scripts decide what to do with the result.
#
# ==============================================================================================
# ── ECOSYSTEM ROLE ────────────────────────────────────────────────────────────────────────────
#
# Kernel Position:
#
#   Kernel/
#     ├── decision_engine.sh
#     ├── transcoding_engine.sh
#     ├── future_engine_modules...
#
# Shared reusable logic belongs in:
#
#   common.sh
#
# Shared ecosystem configuration belongs in:
#
#   master.conf
#
# Host-specific secrets/configuration belong in:
#
#   master_host*.conf
#
# The kernel contains:
#
#   Stateful logic
#   Adaptive systems
#   Scoring systems
#   Cross-domain intelligence
#
# ==============================================================================================
# ── VERSION ───────────────────────────────────────────────────────────────────────────────────
#
# v1.0
#   Initial decision kernel architecture
#   Built first for Lidarr discovery orchestration
#
# ==============================================================================================

# ==============================================================================================
# ── SCORE CANDIDATE ───────────────────────────────────────────────────────────────────────────
# ==============================================================================================
# Calculates weighted score for a media candidate.
#
# Inputs:
#   USER_SCORE
#   POPULARITY_SCORE
#   RECENCY_SCORE
#   QUALITY_SCORE
#
# Output:
#   TOTAL_SCORE
#
# Consumer scripts define actual weighting values.

score_candidate() {

    local user_score="${1:-0}"
    local popularity_score="${2:-0}"
    local recency_score="${3:-0}"
    local quality_score="${4:-0}"

    TOTAL_SCORE=$(( \
        user_score + \
        popularity_score + \
        recency_score + \
        quality_score \
    ))

    echo "$TOTAL_SCORE"
}

# ==============================================================================================
# ── THRESHOLD CHECK ───────────────────────────────────────────────────────────────────────────
# ==============================================================================================
# Determines if candidate passes scoring threshold.
#
# Usage:
#   evaluate_threshold "$score" "$minimum"

evaluate_threshold() {

    local score="$1"
    local minimum="$2"

    if (( score >= minimum )); then
        return 0
    fi

    return 1
}

# ==============================================================================================
# ── TEMPORAL DECAY ────────────────────────────────────────────────────────────────────────────
# ==============================================================================================
# Reduces influence of old behavior over time.
#
# Prevents:
#   Permanent genre lock-in
#   Historical bias accumulation
#   Dead-user dominance
#
# Usage:
#   apply_temporal_decay current_score age_days

apply_temporal_decay() {

    local score="$1"
    local age_days="$2"

    local decay=$(( age_days / 30 ))

    local adjusted=$(( score - decay ))

    (( adjusted < 0 )) && adjusted=0

    echo "$adjusted"
}

# ==============================================================================================
# ── DUPLICATE PROTECTION ──────────────────────────────────────────────────────────────────────
# ==============================================================================================
# Prevents repetitive acquisitions.
#
# Consumer defines:
#   cooldown periods
#   replay windows
#   duplicate tolerance
#
# Returns:
#   0 = duplicate
#   1 = unique

is_duplicate_candidate() {

    local candidate="$1"
    local history_file="$2"

    grep -qi "^${candidate}$" "$history_file" 2>/dev/null
}

# ==============================================================================================
# ── FINAL DECISION ────────────────────────────────────────────────────────────────────────────
# ==============================================================================================
# Produces final engine verdict.
#
# Outputs:
#   ACCEPT
#   REJECT

make_decision() {

    local score="$1"
    local threshold="$2"

    if evaluate_threshold "$score" "$threshold"; then
        echo "ACCEPT"
    else
        echo "REJECT"
    fi
}